In most of projectors which modulate a light emitted from a light source to form an image and projects the image onto a screen or the like to display the image, an OSD (On Screen Display) image such as a menu image, a message image or the like is synthesized and projected onto a principal image (a main image). In Japanese Patent Publication No. 2003-333449, a technique in which a size of letter that is included in the OSD image is changeable is suggested and if the technique is applied, a user can easily see the letter that is included in the OSD image and the letter may be displayed at a suitable size that does not cause a sense of discomfort.
However, in a case where the projector has a zoom adjustment function so as to adjust the size (the display size) of the image that is displayed on the screen or the like, when the display size of the main image is adjusted by the zoom adjustment function, the display size of the OSD image is also changed (enlarged or reduced) together with the main image, such that there is a problem that the OSD image is difficult to see.